Voice coil motors

ABSTRACT

A voice coil motor. A guide bar connects to a fixed base. A coil connects to the fixed base and includes a first winding portion and a second winding portion. A current direction in the first winding portion is opposite that in the second winding portion. A support base movably fits on the guide bar. A magnetic member connects to the support base and includes a first magnetic pole and a second magnetic pole. A magnetization direction of the magnetic member parallels a moving direction of the support base and magnetic member and is perpendicular to a central axis of the coil. The first and second magnetic poles respectively oppose the first and second winding portions of the coil. The first and second magnetic poles respectively interact with the first and second winding portions to generate a first force and a second force, moving the support base and magnetic member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to voice coil motors, and more particularly tovoice coil motors with reduced size, manufacturing costs, and electricalpower consumption and enhanced positioning precision.

2. Description of the Related Art

Cameras disposed in cellular phones have been developed to provide highdefinition quality and reduced power consumption, manufacturing costs,and size. As such, actuators disposed in the cameras, for moving lensmodules thereof, are critical.

Automatic displacement driving devices applied in lens modules mayemploy drivers providing rotational power with a rotational axis thereofparalleling an optical axis of a lens module or drivers providingmovement power with a moving direction thereof paralleling the opticalaxis of the lens module.

An example of a driver providing rotational power with a rotational axisthereof paralleling an optical axis of a lens module is a steppingmotor. The driver requires additional transmission-conversion mechanismsto enable the lens module to move along an optical axis. When the lensmodule arrives at a final position, no electricity is required tomaintain the lens module therein. However, the driver has manycomponents. Thus, the structure of the driver is complicated, and thesize thereof cannot be reduced.

An example of a driver providing movement power with a moving directionthereof paralleling an optical axis of a lens module is a voice coilmotor, a piezoelectric actuator, or a liquid lens actuator. The driverdirectly adjusts the position of the lens module. Compared with thedriver providing rotational power, this driver has fewer components andis small. Nevertheless, there is a need to further reduce the size andenhance precision of this driver.

Taiwan Patent Publication No. 200525859 discloses a voice coil motorwith two opposite non-annular magnets and multiple yoke sets. Thenon-annular magnets and yoke sets form a movable magnetic assembly. Partof the magnetic lines is output from the surface of the non-annularmagnets and is transmitted to a magnetic-permeable shaft via the yokesets, generating radial attraction (radial pre-compression force)between the movable magnetic assembly and the magnetic-permeable shaft.The radial attraction enables the movable magnetic assembly to slidewith respect to the magnetic-permeable shaft in a smooth manner.Moreover, in the voice coil motor, generation of a voice coil forcebetween a coil and the non-annular magnets utilizes part of the magneticlines with the same direction and route.

Referring to FIG. 1A and FIG. 1B, Japan Patent Publication No.2005-128405 discloses a conventional lens driving device 1. An upperspring 9 and a lower spring 11 enable precise movement of a lens module20 and reduce friction during movement thereof. The upper spring 9 andlower spring 11 may be regarded as extensions of the coil 15, serving asconductors at two ends thereof. Specifically, in the lens driving device1, the upper spring 9 and lower spring 11 can provide axialpre-compression force to the lens module 20. Thus, the lens module 20can be easily positioned in a specific position when the coil 15 isenergized by application of a current. Nevertheless, as the lens drivingdevice 1 must comprise a yoke 3 providing magnetic-permeable functions,the size and manufacturing costs thereof cannot be reduced.

Taiwan Patent No. M305361 discloses a voice coil motor having apermanent magnet with a two-pole magnetization direction. Namely, themagnetization direction of the permanent magnet is perpendicular to amoving direction thereof. The permanent magnet with the two-polemagnetization direction can enhance utilization of magnetic flux.Nevertheless, if the shape of the permanent magnet is not a cuboid, thishas further resulting in poor production of the permanent magnet due tothe difficult magnetization. The cost and the size thereof cannot bereduced.

Japan Patent Publication No. 2003-207708, Japan Patent Publication No.2006-220776, and U.S. Pat. No. 5,220,461 disclose voice coil motors witha magnetization direction of a permanent magnet perpendicular to amoving direction thereof (i.e. the permanent magnet is radiallymagnetized). To enhance utilization of magnetic flux from the permanentmagnet, magnetic-permeable yokes are disposed on the radial lateral ofthe permanent magnet. However, reduction of the size of the voice coilmotors is not easily achieved. Moreover, in the voice coil motors, topass a lens module through a coil, the coil must provide a large hollowportion. Accordingly, the winding turns of the coil providing the largehollow portion are limited, adversely affecting enhancement of a voicecoil force. Furthermore, the overall strength of the coil providing thelarge hollow portion is insufficient, causing deformation duringassembly thereof, and further resulting in poor production of the voicecoil motors.

Taiwan Patent Publication No. 200525859 and Taiwan Patent No. 176799disclose voice coil motors with a magnetization direction of a permanentmagnet parallel to a moving direction thereof (namely, the permanentmagnet is axially magnetized). In the voice coil motors, a coil isdisposed between multiple permanent magnets and magnetic-permeable yokesand two gaps exist between a movable part and a fixed part.Specifically, one gap exists between the permanent magnets and the coilwhile the other exists between the magnetic-permeable yokes and thecoil. Due to the two gaps and magnetic-permeable yokes, the size thereofcannot be reduced. Moreover, as guide bars of the voice coil motors arecomposed of magnetic-permeable material, magnetic attraction isgenerated between the guide bars and the permanent magnets, such that astarting current required to overcome sliding friction is increased.Additionally, considerations exist concerning whether there islimitation for the winding turns of the coil and whether disposition ofa sensor matches the outer circumference of the coil.

Hence, there is a need for voice coil motors with reduced size,manufacturing costs, and electrical power consumption and enhancedpositioning precision.

BRIEF SUMMARY OF THE INVENTION

A detailed description is given in the following embodiments withreference to the accompanying drawings.

An exemplary embodiment of the invention provides a voice coil motorcomprising a fixed base, at least one guide bar, at least one coil, asupport base, and at least one magnetic member. The guide bar isconnected to the fixed base. The coil is connected to the fixed base andcomprises a first winding portion and a second winding portion connectedto and opposite the first winding portion. A current direction in thefirst winding portion is opposite to that in the second winding portion.The support base is movably fit on the guide bar. The magnetic member isconnected to the support base and comprises a first magnetic pole and asecond magnetic pole. A magnetization direction of the magnetic memberparallels a moving direction of the support base and magnetic member andis perpendicular to a central axis of the coil. The first and secondmagnetic poles respectively oppose the first and second winding portionsof the coil. The first magnetic pole interacts with the first windingportion to generate a first force. The second magnetic pole interactswith the second winding portion to generate a second force. The firstand second forces drive the support base and magnetic member to movealong the magnetization direction of the magnetic member.

The guide bar comprises non-magnetic-permeable material.

The guide bar is integrally formed with the fixed base.

The voice coil motor further comprises a magnetic-permeable yokedisposed between the support base and the magnetic member.

The voice coil motor further comprises a position sensor connected tothe fixed base and opposing the magnetic member, detecting movement ofthe magnetic member.

The position sensor comprises a Hall sensor, a magnetic resistancesensing element, an electrical sensing element, or a light sensingelement.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1A is a schematic cross section of a conventional lens drivingdevice;

FIG. 1B is an exploded perspective view of the conventional lens drivingdevice of FIG. 1A;

FIG. 2A is an exploded perspective view of a voice coil motor of a firstembodiment of the invention;

FIG. 2B is a perspective assembly view of a lens module and the voicecoil motor of the first embodiment of the invention;

FIG. 3 is a schematic cross section of FIG. 2B;

FIG. 4 is a perspective assembly view of a lens module and a voice coilmotor of a second embodiment of the invention; and

FIG. 5 is a perspective view of a voice coil motor of a third embodimentof the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best-contemplated mode of carryingout the invention. This description is made for the purpose ofillustrating the general principles of the invention and should not betaken in a limiting sense. The scope of the invention is best determinedby reference to the appended claims.

First Embodiment

Referring to FIG. 2A and FIG. 2B, a voice coil motor 101 drives a lensmodule of a camera to perform zoom movement and comprises a fixed base110, two guide bars 120, two coils 130, a support base 140, and twomagnetic members 150. The fixed base 110, guide bars 120, and coils 130may be regarded as fixed members of the voice coil motor 101, while thesupport base 140 and magnetic members 150 may be regarded as movablemembers thereof.

The guide bars 120 are connected to the fixed base 110. Here, the guidebars 120 comprise non-magnetic-permeable material. In this embodiment,the guide bars 120 are integrally formed with the fixed base 110.

The coils 130 are connected to the fixed base 110. As shown in FIG. 2Band FIG. 3, each coil 130 comprises a first winding portion 131 and asecond winding portion 132 connected to and opposite the first windingportion 131. Specifically, as the first winding portion 131 and secondwinding portion 132 construct the loop of each coil 130, a currentdirection in the first winding portion 131 is opposite to that in thesecond winding portion 132.

The support base 140 is movably fit on the guide bars 120. Specifically,as shown in FIG. 2A, the support base 140 comprises two through holes141 in which the guide bars 120 are fit. Namely, the support base 140 isfit on the guide bars 120 via the through holes 141. Moreover, thesupport base 140 can support a lens module L, as shown in FIG. 2B andFIG. 3.

As shown in FIG. 2B and FIG. 3, the magnetic members 150 are connectedto the support base 140. Specifically, a magnetization direction of eachmagnetic member 150 parallels a moving direction of the support base 140and each magnetic member 150 and is perpendicular to a central axis C₁₃₀of each coil 130. Additionally, as shown in FIG. 3, each magnetic member150 comprises a first magnetic pole 151 and a second magnetic pole 152.The first magnetic pole 151 and second magnetic pole 152 oppose thefirst winding portion 131 and second winding portion 132 of each coil130, respectively. Moreover, in this embodiment, the magnetic members150 may be permanent magnets.

Accordingly, the magnetic members 150 provide closed magnetic linesvertically passing through the first winding portion 131 and secondwinding portion 132 of each coil 130. For example, referring to themagnetic member 150 and coil 130 at the right part of FIG. 3, the firstmagnetic pole 151 and second magnetic pole 152 of the magnetic member150 are respectively an S pole and a N pole, the current directions inthe first winding portion 131 and second winding portion 132 of the coil130 are respectively referred to as flowing in and flowing out, and thedirection of the magnetic lines vertically passing through the firstwinding portion 131 is opposite to that vertically passing through thesecond winding portion 132. When the coil 130 is energized byapplication of a current, according to the Lorentz's law, the firstmagnetic pole 151 interacts with the first winding portion 131 togenerate a first force F₁ (i.e. the magnetic lines provided by themagnetic member 150 interact with the current in the first windingportion 131 to generate a first force F₁) and the second magnetic pole152 interacts with the second winding portion 132 to generate a secondforce F₂ (i.e. the magnetic lines provided by the magnetic member 150interact with the current in the second winding portion 132 to generatea second force F₂). Here, the direction of the first force F₁ is thesame as that of the second force F₂. Accordingly, driven by theresultant of the first force F₁ and second force F₂, the support base140 and magnetic members 150 can move along the magnetization directionof the magnetic members 150.

When the voice coil motor 101 is employed to drive a lens module L of acamera to perform zoom movement, the construction is shown in FIG. 2Band FIG. 3. The lens module L is supported by the support base 140 andprovided with an optical axis O. The magnetization direction of themagnetic members 150 parallels the optical axis O. At this point, theresultant of the first force F₁ and second force F₂ generated accordingto the Lorentz's law and parallel to the optical axis O drives the lensmodule L, support base 140, and magnetic members 150 to move along theoptical axis O or magnetization direction of the magnetic members 150.

Moreover, as the guide bars 120 comprise non-magnetic-permeablematerial, no magnetic attraction exists between the guide bars 120 andthe magnetic members 150. Accordingly, when the support base 140 moveson the guide bars 120, friction therebetween is minimal. A startingcurrent required for the voice coil motor 101 to overcome the frictionbetween the support base 140 and the guide bars 120 is thus reduced.

Additionally, the voice coil motor 101 is not limited to having twocoils 130 and two magnetic members 150. Namely, the voice coil motor 101may have merely a coil 130 and a magnetic member 150, achieving the sameeffect of driving the support base 140 and magnetic members 150 to movealong the magnetization direction of the magnetic members 150.

Furthermore, the voice coil motor 101 is not limited to having twomagnetic members 150. Specifically, the voice coil motor 101 may havemerely an L-type magnetic member and the two coils 130 respectivelyoppose two adjacent lateral sides of the L-type magnetic member,achieving the effect of driving the support base 140 and L-type magneticmember to move along the magnetization direction of the L-type magneticmember.

Second Embodiment

Elements corresponding to those in the first embodiment share the samereference numerals.

Referring to FIG. 4, the major difference between this and the firstembodiments is that a voice coil motor 102 of this embodiment furthercomprises a magnetic-permeable yoke 160.

The magnetic-permeable yoke 160 is disposed between the support base 140and the magnetic members 150, enhancing utilization of magnetic fluxfrom the magnetic members 150, and further increasing the first force F₁and second force F₂ generated between the coils 130 and the magneticmembers 150 according to the Lorentz's law.

Structure, disposition, and function of other elements in thisembodiment are the same as those in the first embodiment, andexplanation thereof is omitted for simplicity.

Third Embodiment

Elements corresponding to those in the first embodiment share the samereference numerals.

Referring to FIG. 5, the major difference between this and the firstembodiments is that a voice coil motor 103 of this embodiment furthercomprises a position sensor 170.

The position sensor 170 is connected to the fixed base 110 and opposesone of the magnetic members 150, detecting movement of the magneticmembers 150. In this embodiment, the position sensor 170 may be a Hallsensor, a magnetic resistance sensing element, an electrical sensingelement, or a light sensing element.

Structure, disposition, and function of other elements in thisembodiment are the same as those in the first embodiment, andexplanation thereof is omitted for simplicity.

When the support base 140 and magnetic members 150 move along themagnetization direction of the magnetic members 150, the position sensor170 (Hall sensor or magnetic resistance sensing element) detects theintensity of a magnetic field, in a fixed position in the voice coilmotor 103, provided by the magnetic members 150. Here, the intensity ofthe magnetic field, in the fixed position, provided by the magneticmembers 150 is related to displacement of the magnetic members 150. Bycombining the position sensor 170 with a positioning controller (notshown), closed-loop positioning control can be obtained. The movingposition of the support base 140 and magnetic members 150 is thuscontrolled.

In conclusion, the disclosed voice coil motors provides the followingadvantages. Based upon the aforementioned arrangement of the coils andmagnetic members, the magnetic lines provided with different directionsor routes can be simultaneously utilized, thereby increasing theresultant (first force F₁ and second force F₂) generated according tothe Lorentz's law. Further, Based upon the aforementioned arrangement ofthe coils and magnetic members, the magnetic lines provided withdifferent directions or routes can be simultaneously utilized, therebyenhancing the utilization of the magnetic flux. Thus, the voice coilmotors can generate a sufficient voice coil force in the absence of amagnetic-permeable yoke, such that the size and manufacturing costs ofthe voice coil motors can be reduced. Moreover, as hollow portions ofthe coils are not penetrated by members, the size of the hollow portionsis reduced. Namely, the coils are provided with increased winding turns,enhancing the voice coil force and providing enhanced overall strength.Alternatively, as the hollow portions of the coils are penetrated by nomember, the size of the hollow portions is reduced, thereby reducing theoverall size of the voice coil motors. Additionally, only one gap existsbetween the magnetic members (fixed members) and the coils (movablemembers), such that the voice coil motors can be miniaturized.Furthermore, as disposition of the position sensor is not confined bythe size and position of the coils, the arrangement of the members inthe voice coil motors is flexible, advantageously reducing the overallsize of the voice coil motors.

While the invention has been described by way of example and in terms ofpreferred embodiment, it is to be understood that the invention is notlimited thereto. To the contrary, it is intended to cover variousmodifications and similar arrangements (as would be apparent to thoseskilled in the art). Therefore, the scope of the appended claims shouldbe accorded the broadest interpretation so as to encompass all suchmodifications and similar arrangements.

1. A voice coil motor, comprising: a fixed base; at least one guide bar connected to the fixed base; at least one coil connected to the fixed base and comprising a first winding portion and a second winding portion connected to and opposite the first winding portion, wherein a current direction in the first winding portion is opposite to that in the second winding portion; a support base movably fit on the guide bar; and at least one magnetic member connected to the support base and comprising a first magnetic pole and a second magnetic pole, wherein a magnetization direction of the magnetic member parallels a moving direction of the support base and magnetic member and is perpendicular to a central axis of the coil, the first and second magnetic poles respectively oppose the first and second winding portions of the coil, the first magnetic pole interacts with the first winding portion to generate a first force, the second magnetic pole interacts with the second winding portion to generate a second force, and the first and second forces drive the support base and magnetic member to move along the magnetization direction of the magnetic member.
 2. The voice coil motor as claimed in claim 1, wherein the guide bar comprises non-magnetic-permeable material.
 3. The voice coil motor as claimed in claim 1, wherein the guide bar is integrally formed with the fixed base.
 4. The voice coil motor as claimed in claim 1, further comprising a magnetic-permeable yoke disposed between the support base and the magnetic member.
 5. The voice coil motor as claimed in claim 1, further comprising a position sensor connected to the fixed base and opposing the magnetic member, detecting movement of the magnetic member.
 6. The voice coil motor as claimed in claim 5, wherein the position sensor comprises a Hall sensor, a magnetic resistance sensing element, an electrical sensing element, or a light sensing element. 